The present invention relates to a new and improved method for synchronizing a receiver end-Key Generator with a transmitter end-Key Generator and further pertains to apparatus for the performance of the aforesaid method.
There are known to the art enciphering devices and deciphering devices equipped with Key Generators (key character generators) which produce a train of Key pulses. These Key pulses are coupled in conventional manner with the pulses of the text or message which is to be enciphered to deciphered, respectively. As a generaly rule the Key Generators are stepped forward by one step for each bit which is to be enciphered or deciphered, respectively, so that there is insured for the required synchronization between the Key Generator located at the receiver (receiver end) and the Key Generator located at the transmitter (transmitter end). For the enciphering or deciphering respectively, of a new bit there is thus always utilized a new Key bit of the Key pulse train.
At the present time the following three requirements, among others, are placed upon the Key Generators:
1. High operating speed. PA1 2. Complicated formation principle for producing the Key pulse train. PA1 3. Extremely long period of the Key pulse train sequence.
The first demand or requirement listed above is placed by virtue of the transmission technology presently in existence, whereas the second and third requirements exist for security reasons since decrypting of an enciphered text or message by unauthorized individuals must be rendered impossible even when using the most modern devices or aids.
For proper deciphering it is necessary that at the start of transmission of a message of the Key Generators at both the transmitter end and the receiver end have the same starting position. In other words the Key pulse train of the receiver end-Key Generator should be at the same location as the Key pulse train at the transmitter end-Key Generator.
This synchronization of the Key Generators at the transmitter end and the receiver end at the start of message transmission is particularly problematic in the case of meshed or interconnected networks where there are transmitted in different directions always between different stations messages of high information content. If for instance station A has transmitted a message to station B during a predetermined time duration T, e.g. 20 seconds, with a clock frequency of 5 MHz, then as above explained, the Key Generators of these stations A and B have been stepped forward by a number of steps corresponding to the length of the transmitted message and have assumed a different position of the Key pulse sequence. Now if station A or station B should transmit a message to station C which was not in operation during the aforementioned time duration T, then it should be apparent that first of all the Key Generator of such station C must be brought into synchronism with the Key Generator of the station A or station B, as the case may be. In other words for the aforementioned numerical example the Key Generator of the station C must be stepped forward 20.5.multidot.10.sup.6 steps. This adjustment of the Key Generator should however occur for practical reasons without time-delay. If the adjustment should take place for instance within 0.1 seconds, then this means that the Key Generator must be stepped with a clock frequency of 1 GHz. Yet, in practice this is not possible for physical reasons. It is for this reason that up to the present there have not been devised any enciphering- and deciphering devices which can be employed in the above explained manner for relatively high transmission speeds.